1. Field of the Invention
The present invention relates generally to an apparatus for alternately releasing and holding a side gear of a differential assembly against rotation relative to a case. More particularly, the invention pertains to electromagnetic actuation of a device for releasing and holding the side gear.
2. Description of the Prior Art
A locking differential is used to prevent relative rotation of one driven wheel with respect to another driven wheel. This is usually accomplished by locking one differential side gear to a differential case, thereby preventing rotation of the side gear with respect to the differential case and preventing a wheel speed differential on any one axle.
A locking differential employs hydraulic pressure or an electromagnet to actuate a mechanism that alternately holds a side gear against rotation and releases the side gear to rotate freely. Due to packaging constraints, however, certain vehicle applications require a small electromagnetic coil whose size and number of windings may not provide an engagement force of sufficient magnitude to lock the differential. In such instances, a technique is required to amplify the actuating force produce by the coil to a magnitude that is sufficient to produce reliable, axial displacement of the coil.
The actuating force produced by the coil varies non-linearly and inversely with air gap. Thus for a given coil size, the initial air gap should be kept as small as possible in order to maximize the force that actuates the differential to the locked condition.
A need exists in the industry for a locking differential actuated by a small axially displaceable electromagnetic coil having a minimum air gap such that displacement of the coil is amplified producing greater displacement for a locking mechanism that secures one of the side gears of the differential against rotation on a differential case.